Strapping machines apply a steel or polymeric strap in a sealed tensioned loop about a package to securely bind the package for shipping, storage and merchandising. Automatic strapping machines generally comprise an automatic strap feeding mechanism that initially feeds the strap to a strap application assembly comprising an annular channel, or strap receiving chute where the strap is formed in a loop which surrounds a package to be bound. An automatic strap tensioning mechanism then applies a tension to the strap so that the strap application assembly may form a strap seal to securely bind the package. Steel straps are typically sealed with a metal clip, and polymeric straps are typically sealed by a weld formed with a heated blade or by friction. It has been suggested to feed the strap to the strap application assembly by frictionally engaging the strap between a pair of counter-rotating rollers rotated by a motor driven shaft journaled to a frame. Likewise, it has also been suggested to apply a tension to the strap by frictionally engaging the strap between a pair of counter-rotating rollers that draw the strap in a tight loop about the package. For example, U.S. Pat. No. 3,232,217 to Harmon et al. discloses a strap feeding and tensioning mechanism comprising two pair of counter-rotating rollers mounted on a bracket that may be positioned to frictionally engage a strap for feeding or tensioning the strap in a strap application assembly. Automatic strapping machines however frequently encounter problems feeding the strap to the strap application assembly. For instance, the strap may not properly feed along the annular channel due to an obstruction which may be caused by the packaging, or bundle, in the strap application assembly. A strap obstructed by the strap application assembly during feeding of the strap may accumulate and become entangled in the strap feeding and tensioning apparatus. Similarly, a strap not securely retained by the strap application assembly during tensioning will be retracted from the strap application assembly, and may also accumulate and become entangled in the strap feeding and tensioning apparatus. The misfed strap must then be re-fed by the strap feeding mechanism, which, in the past, has required a manual re-feeding of the strap by a technician at a substantial loss of productivity. Also, known strap feeding and tensioning mechanisms have the disadvantage that they subject the strap to considerable mechanical stress that may result in breakage of the strap during application of the strap or during handling of the bound package. Mechanical stress is not limited to the strap, but also to the strap feeding and particularly the strap tensioning mechanism, which may be subject to considerable frictional forces during feeding and tensioning of the strap. There exists therefore a demonstrated need for an advancement in the art of feeding and tensioning a strap in a strapping machine.
It is an object of the present invention to provide a novel strap feeding and tensioning apparatus.
It is another object of the invention to provide a novel strap feeding and tensioning apparatus that automatically re-feeds a strap not properly fed to a strap application assembly in the first instance.
It is another object of the invention to provide a novel strap feeding and tensioning apparatus having a strap overflow housing for receiving a strap that is prevented from properly feeding to a strap application assembly.
It is also an object of the invention to provide a novel strap feeding and tensioning apparatus having a strap stretch-out housing for receiving a strap that is removed from the strap application assembly during tensioning of the strap.
It is also an object of the invention to provide a novel strap feeding and tensioning apparatus that is economical to manufacture and, easy to operate.
It is another object of the invention to provide a novel strap feeding and tensioning apparatus that minimizes damage to a strap during feeding and tensioning of the strap.
It is a further object of the invention to provide a novel strap feeding and tensioning apparatus having a cam actuated feed roller that feeds the strap to a strap application assembly.
It is a further object of the invention to provide a novel strap feeding and tensioning apparatus having a cam actuated tensioning roller that applies a fixed or variable tension on the strap after the strap is formed in a loop in a strap application assembly.
It is a further object of the present invention to provide a novel strap feeding and tensioning apparatus that reduces an amount of energy required to feed and apply tension to the strap.
It is yet a further object of the invention to provide a novel strap feeding and tensioning apparatus that reduces stress on the feeding and tensioning apparatus and thereby increases the reliability and lifetime of the strap feeding and tensioning apparatus.
Accordingly, the present invention is directed toward a novel method and apparatus for feeding and tensioning a strap in a power strapping machine. The apparatus includes a strap feeding mechanism, a strap tensioning mechanism, a pivoting roller carriage having a cam follower, a strap overflow housing for receiving a strap that is prevented from properly feeding to the strap application assembly, and a strap stretch-out housing for receiving a strap that is removed from the strap application assembly during tensioning of the strap. The overflow housing and the stretch-out housing retain the strap free of kinks and entanglement. The strap feeding mechanism is comprised of a fixed feed drive roller and a feed follow roller disposed on the pivoting roller carriage. The strap tensioning roller is comprised of a fixed tension drive roller and a tension follow roller also disposed on the pivoting roller carriage. The pivoting roller carriage is pivoted by a feeding and tensioning cam having a feed phase stirface and a tension phase surface. The feed phase surface engages the cam follower and pivots the pivoting roller carriage to actuate the strap feeding mechanism to engage a portion of a strap and feed the strap toward a strap application assembly where the strap is formed in a loop about a package. The strap feeding and tensioning mechanism actuates a first gripper that secures an end of the strap in the strap application assembly. The tension phase surface of the cam then engages the cam follower and pivots the pivoting roller carriage to actuate the strap tensioning mechanism to engage a portion of the strap and apply a tension to the looped strap. The strap feeding and tensioning apparatus also actuates a second gripper that secures the tensioned strap in a closed loop about the package so that the strap application assembly may form a strap joint sealing the strap in the closed loop. In the event that the strap is not properly engaged by the first gripper, or the strap is retained in the overflow housing due to an obstruction in the strap application assembly, the strap will be fully retracted from the strap application assembly or the overflow housing, and directed into tile strap stretch-out housing where it will remain until the feeding surface again engages the cam follower and pivots the pivoting roller carriage to actuate the strap feeding mechanism to engage a portion of the strap and re-feed the strap toward the strap application assembly. The apparatus automatically re-feeds the strap to the strap application assembly if the strap is obstructed, or not properly secured by the first gripper, in the first instance. In one embodiment, the weight and position of the strap disposed in the strap stretch-out housing disposed above the feeding and tensioning mechanism prevents the strap from entirely withdrawing from the strap feeding mechanism, thereby ensuring that the strap feeding mechanism will engage and re-feed the strap to the strap application assembly. In another embodiment, the stretch-out housing is disposed below the feeding and tensioning mechanism, and the strap is folded over on itself in the housing, which gives rise to an upward springing action that prevents the strap from becoming disengaged from the feeding mechanism. A one way strap guide, or finger, prevents the strap from returning to a strap dispenser coil, or supply, and guides the strap into the stretch-out housing during tensioning of the strap.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following Detailed Description of the Invention with the accompanying drawings.